Chiral phenol derivative, liquid crystal medium containing said chiral phenol derivative

ABSTRACT

The invention relates to chiral phenols, preferably of formula (I), the different parameters having the meaning indicated in the description, liquid crystal media which contain said compounds as chiral doping agents and/or stabilizers, and the use thereof in electro-optical displays.

The present invention relates to chiral phenol derivatives and toliquid-crystalline media which comprise these compounds. The presentinvention also relates to a process for the chiral doping andsimultaneous stabilisation of liquid-crystal mixtures. The presentinvention furthermore relates to liquid-crystal displays which containthe liquid-crystal mixtures according to the invention.

In the known liquid-crystal displays, the liquid crystals, generallyliquid-crystalline mixtures, are used as dielectrics whose opticalproperties change reversibly on application of an electric voltage.These liquid-crystal displays use various electro-optical effects. Thecommonest of these are the TN (twisted nematic) effect, with ahomogeneous, virtually planar initial alignment of the liquid crystalsand a nematic structure twisted by about 90°), the STN effect(supertwisted nematic) and the SBE effect (super-twisted birefringenceeffect), both of which, like the TN effect, use a twisted, homogeneousinitial alignment of the liquid crystals, but here the molecules have asignificant surface tilt angle (“tilt angle” for short) at the surfaceof the substrates, and the twist between the substrates is significantlygreater than 90°. In this application, unless explicitly statedotherwise, the STN effect and the SBE effect below are both jointlyreferred to as the STN effect. The tilt angle at the surface in STNdisplays is typically between 2° and 10°. It is greater the greater thetwist angle. The twist angles are generally about 180° to 240°,sometimes also up to 260° or 270° and in some cases even greater.

The twist of the liquid-crystal medium by greater than 90° is achievedthrough the use of chiral liquid-crystal mixtures whose natural twist isselected in accordance with the layer thickness of the liquid-crystallayer. To this end, two possibilities are available to the personskilled in the art. The first consists in the use of liquid crystalswhich are themselves chiral, i.e. cholesteric liquid crystals. Suchliquid crystals themselves have a twisted structure. In a homogeneouslyaligned arrangement between two substrates, which is known as theGrandjean texture, the director of the molecules is helically twisted inthe vertical direction, i.e. over the thickness of the layer.

The characteristic length for a complete rotation through 360° is knownas the cholesteric pitch (P). However, the use of cholesteric liquidcrystals is often not particularly advantageous since the cholestericpitch of cholesteric liquid crystals cannot be matched easily to thelayer thicknesses of the display cells usually used. In addition, thecholesteric pitch of these liquid crystals is often disadvantageouslyand in many cases highly dependent on the temperature. A change in thecomposition of the mixtures also usually results in considerable changesin the cholesteric pitch.

For this reason, in most practical cases a chiral substance whichinduces the desired twist is added to a nematic liquid-crystal mixture.It is not particularly important here whether this compound itself has amesophase. Rather, it is more important that it has a high twistingpower for the nematic base mixture (also known as host mixture) and thatit does not change the properties of the base mixture, in particular itsclearing point, excessively in the concentrations usually employed.Preference is thus generally given to the use of compounds whichthemselves have a mesogenic structure or are even cholesteric.

The cholesteric phases which are induced by addition of chiralsubstances to nematic liquid crystals are often known as chirallynematic phases. In the present application, however, these are alsoreferred to as cholesteric phases, unless explicitly stated otherwise.

The cholesteric pitch induced by addition of chiral substances (dopants)to nematic liquid crystals is dependent at a given temperature, besideson the enantiomeric purity of the chiral dopant, in particular on thedopant concentration (c) employed and on the twisting power of thedopant. This twisting power is known as the HTP (helical twistingpower). To a first approximation, the induced cholesteric pitch (P) isinversely proportional to the product of HTP and dopant concentrationemployed, as shown in equation (1).P=(HTP·c)⁻¹  (1)

In STN displays, use is typically made of liquid-crystal mixtures havinga cholesteric pitch to layer thickness ratio (d/P) in the range from 0.4to 0.8, frequently of about 0.5.

However, chiral liquid-crystal mixtures are also used in TN displays,here in order to avoid twist in the reverse direction (reverse twist).Occurrence of this would result in the formation of domains and thus ina reduction in contrast. In TN displays, use is generally made ofcholesteric liquid-crystal mixtures having a significantly smaller d/Pratio than in STN displays since larger d/P values in most cases resultin an increase in the threshold voltage. The values here are typicallyabout 0.01 to 0.3, frequently about 0.1.

Besides these display types, there are further liquid-crystal displayswhich use liquid-crystal mixtures doped with chiral compounds.

Known chiral dopants are, for example, the compounds C15, CB15, R-811and S-811, R-1011 and S-1011, and R-2011 and S-2011, all Merck KGaA.

In these and similar electro-optical effects, use is made ofliquid-crystalline media of positive dielectric anisotropy (Δ∈).

Besides the electro-optical effects mentioned which requireliquid-crystal media of positive dielectric anisotropy, there are otherelectro-optical effects which use liquid-crystal media of negativedielectric anisotropy, such as, for example, the ECB (electricallycontrolled birefringence) effect and its sub-forms DAP (deformation ofaligned phases), VAN (vertically aligned nematics) and CSH (colour superhomeotropics). In these and similar electro-optical effects, use is madeof liquid-crystalline media of negative dielectric anisotropy (Δ∈).

An electro-optical effect having excellent, low viewing-angle dependenceof the contrast uses axially symmetrical micropixels (ASMs). In thiseffect, the liquid crystal of each pixel is surrounded cylindrically bya polymer material. This mode is particularly suitable for combinationwith addressing through plasma channels. In particular, large-area PALCDs having good viewing-angle dependence of the contrast can beachieved in this way.

The IPS (in plane switching) effect employed to an increased extentrecently can use both dielectrically positive and dielectricallynegative liquid-crystal media, similar to guest-host displays, which canemploy dyes either in dielectrically positive or in dielectricallynegative media, depending on the display mode used.

The pixels of the liquid-crystal displays can be addressed directly,time-sequentially, i.e. in time-multiplex mode, or by means of a matrixof active, electrically non-linear elements.

The commonest AMDs (active matrix displays) hitherto use discrete activeelectronic switching elements, such as, for example, three-poleswitching elements, such as MOS (metal oxide silicon) transistors orthin-film transistors (TFTs) or varistors or 2-pole switching elements,such as, for example, MIMs (metal insulator metal) diodes, ring diodesor back-to-back diodes. In the TFTs, various semiconductor materials,predominantly silicon or alternatively cadmium selenide, are used. Inparticular, amorphous silicon or polycrystalline silicon is used.

Some liquid-crystalline compounds and some mesogenic compounds havingotherwise technically favourable properties are not sufficiently stablefor use in practical liquid-crystal displays. There are various reasonsfor the inadequate stability of the various compounds. These may be dueto inadequate stability of the compounds to UV radiation and/or visiblelight or to their inadequate stability to thermal loads.

Some compounds react with even traces of oxygen. This takes place fasterat higher temperatures. In the case of liquid-crystal mixtures whichcomprise compounds of this type, the stability to thermal loads, andthus the life of the displays, can be significantly increased by addingcorresponding stabilisers.

Thus, DE 195 391 41 and DE 101 172 24 propose a phenol of the formula

as stabiliser for liquid-crystal mixtures of this type. These compoundsare not chiral and are thus not suitable for inducing a cholestericphase in nematic liquid crystals.

If it is intended to use liquid-crystal mixtures which compounds havingrelatively low stability to thermal loads in the presence of oxygen indisplays which require cholesteric liquid crystals, both a chiral dopantand a stabiliser must be added to the nematic base mixtures. This meansat least two additional steps in the production of mixtures of thistype.

There is thus a demand for compounds which allow the desired cholestericpitch to be induced in nematic base mixtures and at the same time allowthese mixtures to be stabilised.

It has been found that this requirement can be achieved through the useof corresponding compounds.

Compound of the formula I

-   -   in which    -   R*¹ denotes a chiral radical,    -   Z¹, if present more than once, in each case, independently of        one another, denotes —CH₂—CH₂—, —CH═CH—, —C≡C—, —COO—, —OCO—,        —CH₂O—, —OCH₂—, —CF₂O—, —OCF₂—, —(CH₂)₄—, —CF═CF—, —CH═CF—,        —CF═CH—, —CH₂—, —CF₂—, —CHF—, —O—, —S— or a single bond,

-   -   -   if present more than once, in each case,        -   independently of one another, denotes

    -   (a) a trans-1,4-cyclohexylene radical, in which, in addition,        one or more non-adjacent CH₂ groups may be replaced by —O—        and/or —S—,

    -   (b) a 1,4-cyclohexenylene radical,

    -   (c) a 1,4-phenylene radical, in which, in addition, one or two        CH groups may be replaced by N, or

    -   (d) a radical selected from the group consisting of        1,4-bicyclo[2.2.2]octylene, piperidine-1,4-diyl,        naphthalene-2,6-diyl, decahydronaphthalene-2,6-diyl and        1,2,3,4-tetrahydronaphthalene-2,6-diyl,

    -   where these radicals (a) to (d) and the phenolic benzene ring        may optionally be mono- or polysubstituted by F atoms, and

    -   n¹ denotes 0, 1, 2 or 3.        have proven particularly suitable.

In the formula I,

-   -   if present more than once, in each case, independently of one        another, preferably denotes

-   -   Z¹, if present more than once, in each case, independently of        one another, preferably denotes —CH₂—CH₂—, —CH═CH—, —C≡C—, —COO—        or a single bond, particularly preferably —CH₂—CH₂— or a single        bond, especially preferably a single bond, and    -   n¹ preferably denotes 0, 1 or 2, preferably 0 or 1.

Preference is furthermore given to compounds of the formula Ia

-   -   in which    -   R*¹ and

have the meaning given above in the case of the formula I, and

-   -   Z¹¹ and Z¹² each, independently of one another, have the meaning        given above for Z¹ in the case of the formula I,    -   and    -   n¹¹ denotes 0, 1 or 2, preferably 0 or 1, and    -   W, X, Y and Z each, independently of one another, denote H, F,        Cl, alkyl or alkoxy, preferably having 1 to 7 C atoms.

Preference is furthermore given to compounds of the formula I,preferably of the formula Ia, characterised in that

-   -   R*¹ denotes a chiral radical of the formula

-   -   in which    -   K denotes a single bond, alkylene having 1 to 9, preferably        having 1 to 5 C atoms, alkenylene or alkynylene having 2 to 9,        preferably having 2 to 5 C atoms, where one, two or more of the        —CH₂— groups present in all three types of group may each be        replaced by —O—, —C═O— or —S—, but where no two O atoms are        bonded directly to one another and all three types of group may        optionally be substituted by halogen, preferably by fluorine,        and K preferably denotes a single bond, —CH₂—, —O—, —CO—O—,        —CO—O—CH₂—, —O—CO—, —CH₂—CH₂—, —CH═CH— or —C≡C—, and    -   L, M and N, each independently of one another, but differently        from one another and from the remainder of the molecule        including the group K, denote hydrogen, halogen, preferably F,        aryl or cycloalkyl, alkyl or alkoxy having 1 to 11, preferably 1        to 7 C atoms, alkenyl, alkenyloxy, alkynyl or alkynyloxy having        2 to 11, preferably 2 to 7 C atoms, where one, two or more of        the —CH₂— groups present in all six types of group may each be        replaced by —O—, —C═O— or —S—, but where no two O atoms are        bonded directly to one another and all six types of group may        optionally be substituted by halogen, preferably by fluorine,        and L, M and/or N preferably denote phenyl, alkyl, alkoxy,        alkenyl or alkynyl.

In these compounds,

-   -   R*¹ denotes in particular a chiral radical selected from the        group consisting of the radicals of the formulae

-   -   -   in which

    -   Q denotes H or halogen, preferably H or F, in particular H,

    -   n and m are different from one another and otherwise,        independently of one another, denote 1 to 11,

    -   p denotes 0 or 1, and

    -   r denotes 0 to 4, preferably 0 to 2.

Preferably denotes

-   -   in which the parameters have the meaning given above.

Particular preference is given to compound of the formula Ia selectedfrom the group consisting of the compounds of the formulae Ia-1 to Ia-9

-   -   in which the parameters have the meaning given above, and    -   W and Z preferably denote H.

The compounds of the formula I are prepared in accordance with scheme Iand II.

in which “R chir.” denotes R*¹, and the parameters have the meaninggiven above under the formula I.

in which “R chir.” denotes R*¹, and the parameters have the meaninggiven above under the formula I.

The liquid-crystal media according to the invention comprise one or morecompounds of the formula I.

In a preferred embodiment, the liquid-crystal media in accordance withthe present invention comprise

a) one or more chiral compounds of the formula I

b) one or more dielectrically neutral compounds of the formula II

-   -   in which    -   R²¹ and R²² each, independently of one another, denote H, an        alkyl group having 1 to 15 C atoms which is monosubstituted by        CN or CF₃ or at least monosubstituted by halogen, in which, in        addition, one or more CH₂ groups may each, independently of one        another, be replaced by —O—, —S—, —CH═CH—, —CF═CF—, —CF═CH—,        —CH═CF—,

—CO—, —CO—O—, —O—CO— or —O—CO—O— in such a way that O atoms are notlinked directly to one another, preferably alkyl and alkoxy having 1 to12 C atoms, alkoxyalkyl, alkenyl or alkenyloxy having 2 to 12 C atoms,

-   -   Z²¹ and Z²² each, independently of one another, have the meaning        given above for Z¹¹ in the case of the formula I,

each, independently of one another, denote

particularly preferably, if present, denote

I denotes 0 or 1,andc) one or more dielectrically positive compounds ord) one or more dielectrically negative compoundsand optionallye) one or more dielectrically neutral compound(s).

The liquid-crystal media in accordance with the present inventionpreferably comprise one or more compounds having at least one olefinicdouble bond and/or containing at least one —CF_(z)—O— group. Preferenceis given to the compounds which have at least one olefinic double bond,dielectrically positive or dielectrically neutral.

Particular preference is given to dielectrically neutral compounds ofthe formula II, in which at least one of the following conditions ispreferably met:

a) R²¹ denotes alkenyl,

b) R²² denotes alkenyl and

c) at least one of the bridges Z²¹ and Z²² present denotes —CH═CH—.

The liquid-crystal media preferably comprise one or more compounds ofthe formula II which contain no biphenyl unit.

The liquid-crystal media particularly preferably comprise one or morecompounds of the formula II

-   -   in which two adjacent rings are    -   linked directly and preferably denote

The liquid-crystal medium preferably comprises one or more compoundsselected from the group consisting of the compounds of the formulae II1to II4

-   -   in which    -   R²¹ and R²² each have the meaning given above in the case of the        formula II, and at least one of the groups R²¹ and R²² in the        formula II1 preferably denote alkenyl. Preferably, R²¹ is alkyl        or alkoxy having 1-5 C atoms and R²² is alkenyl.

Here, as throughout the present application, unless expressly statedotherwise, the term compounds, for clarification also written ascompound(s), denotes both one compound and a plurality of compounds.

The liquid-crystal medium preferably comprises one or more compounds ofthe formula III

-   -   in which    -   R³ denotes alkyl or alkoxy having 1 to 7 C atoms, alkenyl,        alkenyloxy or oxaalkyl having 2 to 7 C atoms, preferably alkyl        or alkenyl, preferably having 1 to 5 or 2 to 5 C atoms        respectively,

-   -   -   each, independently of one another, denote

-   -   -   preferably

-   -   X³ denotes F, Cl, —OCF₂H, —OCF₃ or —CF₃, preferably F, Cl or        —CF₃, and    -   Y³¹ and Y³² each, independently of one another, denote H or F.

The liquid-crystal medium preferably comprises one or more compounds ofthe formula III selected from the group consisting of the compounds ofthe formulae III1 to III5, preferably III1, III4 and III5, particularlypreferably III1 and III5,

in which the parameters have the meaning given above under the formulaIII, and preferably

-   -   R³ denotes alkyl or alkenyl and    -   X³ and Y³¹ both denote F and Y³² denotes H or F, preferably F,        or    -   X³ denotes —OCF₃ and Y³¹ denotes F and Y³² denotes H or F,        preferably H.

In the case of the nematic or nematogenic compounds, in particular inthe case of the compounds of the formulae II and III, the individualcompounds are generally employed in concentrations of 1% to 30%,preferably 2% to 20% and particularly preferably 4% to 16%.

In a particularly preferred embodiment, which may be identical andpreferably is identical with the above-described preferred embodimentsfor the preferred concentration ranges, the liquid-crystal mediacomprise

-   -   one or more compounds of the formula Ia and    -   one or more compounds of the formula II, preferably selected        from the group consisting of the compounds of the formulae II2        to II4, and/or    -   one or more compounds of the formula III, preferably selected        selected from the group consisting of the compounds of the        formulae III1 and III5.

The liquid-crystal media according to the invention preferably each havenematic phases at least from −10° C. to 70° C., preferably from −30° C.to 80° C. and very particularly preferably from −40° C. to 90° C. Theterm “have a nematic phase” here means firstly that no smectic phase andno crystallisation is observed at low temperatures at the correspondingtemperature and secondly also that no clearing occurs on heating fromthe nematic phase. The investigation at low temperatures is carried outin a flow viscometer at the corresponding temperature and checked bystorage in test cells having a layer thickness corresponding to theelectro-optical application for at least 100 hours. At hightemperatures, the clearing point is measured in capillaries byconventional methods.

In addition, the liquid-crystal media according to the invention haverelatively small values for the Freedericksz threshold voltage of lessthan or equal to 3.0 V, preferably less than or equal to 2.0 V,particularly preferably less than or equal to 1.5 V and veryparticularly preferably less than or equal to 1.0 V.

These preferred values for the individual physical properties are alsoobserved in each case combined with one another. Thus, media accordingto the invention have, in particular, the following propertycombinations:

The term “alkyl” preferably covers straight-chain and branched alkylgroups having 1-7 carbon atoms, in particular the straight-chain groupsmethyl, ethyl, propyl, butyl, pentyl, hexyl and heptyl. Groups having2-5 carbon atoms are generally preferred.

The term “alkenyl” preferably covers straight-chain and branched alkenylgroups having 2-7 carbon atoms, in particular the straight-chain groups.Particularly preferred alkenyl groups are C₂-C₇-1 E-alkenyl,C₄-C₇-3E-alkenyl, C₅-C₇-4-alkenyl, C₆-C₇-5-alkenyl and C₇-6-alkenyl, inparticular C₂-C₇-1 E-alkenyl, C₄-C₇-3E-alkenyl and C₅-C₇-4-alkenyl.Examples of further preferred alkenyl groups are vinyl, 1 E-propenyl, 1E-butenyl, 1 E-pentenyl, 1E-hexenyl, 1E-heptenyl, 3-butenyl,3E-pentenyl, 3E-hexenyl, 3E-heptenyl, 4-pentenyl, 4Z-hexenyl,4E-hexenyl, 4Z-heptenyl, 5-hexenyl, 6-heptenyl and the like. Groupshaving up to 5 carbon atoms are generally preferred.

The term “fluoroalkyl” preferably covers straight-chain groups having aterminal fluorine, i.e. fluoromethyl, 2-fluoroethyl, 3-fluoropropyl,4-fluorobutyl, 5-fluoropentyl, 6-fluorohexyl and 7-fluoroheptyl.However, other positions of the fluorine are not excluded.

The term “oxaalkyl” or “alkoxyalkyl” preferably covers straight-chainradicals of the formula C_(n)H_(2n+1)—O—(CH₂)_(m), in which n and meach, independently of one another, denote 1 to 6. n is preferably=1 andm is preferably 1 to 6.

In the present application, the term dielectrically positive compoundsmeans compounds having a Δ∈>1.5, dielectrically neutral compounds meansthose in which −1.5≦Δ∈≦1.5, and dielectrically negative compounds meansthose having a Δ∈<−1.5. The dielectric anisotropy of the compounds isdetermined here by dissolving 10% of the compounds in aliquid-crystalline host and determining the capacitance of this mixtureat 1 kHz in at least one test cell having a density of 10 μm with ahomeotropic surface alignment and in at least one test cell having adensity of 10 μm with a homogeneous surface alignment. The measurementvoltage is typically 0.5 V to 1.0 V, but is always less than thecapacitive threshold of the respective liquid-crystal mixture.

The host mixture used for dielectrically positive compounds is ZLI-4792and the host mixture used for dielectrically neutral and dielectricallynegative compounds is ZLI-3086, both from Merck KGaA, Germany. Thechange in the dielectric susceptibilities of the host mixture afteraddition of the compound to be investigated and extrapolation to 100% ofthe compound employed gives the values for the respective compounds tobe investigated.

The term threshold voltage usually relates to the optical threshold for10% relative contrast (V₁₀).

In relation to the liquid-crystal mixtures of negative dielectricanisotropy, however, the term threshold voltage in the presentapplication is used for the capacitive threshold voltage (V₀), alsoknown as the Freedericksz threshold, unless explicitly stated otherwise.

All concentrations in this application, unless explicitly statedotherwise, are given in percent by weight and relate to thecorresponding mixture as a whole. All physical properties are and havebeen determined in accordance with “Merck Liquid Crystals, PhysicalProperties of Liquid Crystals”, status Nov. 1997, Merck KGaA, Germany,and apply to a temperature of 20° C., unless explicitly statedotherwise. Δn is determined at 589 nm and Δ∈ at 1 kHz. The thresholdvoltages and the other electro-optical properties were determined intest cells produced at Merck KGaA, Germany, using white light by meansof a commercial measuring instrument from Otsuka, Japan. To this end,cells were selected having, depending on the Δn of the liquid crystals,a thickness corresponding to an optical retardation d·Δn of the cells ofabout 0.50 μm. The cells were operated in so-called “normally whitemode” with polarisers parallel to the rubbing directions on the adjacentsubstrates. The characteristic voltages were all determined withperpendicular viewing. The threshold voltage has been indicated as V₁₀for 10% relative contrast, the mid-grey voltage V₅₀ for 50% relativecontrast and the saturation voltage V₉₀ for 90% relative contrast.

In the case of the liquid-crystal media of negative dielectricanisotropy, the threshold voltage was determined as the capacitivethreshold V₀ (also known as the Freedericksz threshold) in cells with aliquid-crystal layer aligned homeotropically by means of lecithin.

The liquid-crystal media according to the invention may, if necessary,also comprise further additives and optionally also further chiraldopants in the conventional amounts. The amount of these additivesemployed is in total 0% to 10%, based on the amount of the mixture as awhole, preferably 0.1% to 6%. The concentration of the individualcompounds employed is preferably 0.1 to 3%. The concentration of theseand similar additives is not taken into account when indicating theconcentrations and the concentration ranges of the liquid-crystalcompounds in the liquid-crystal media.

The compositions consist of a plurality of compounds, preferably 3 to30, particularly preferably 6 to 20 and very particularly preferably 10to 16 compounds, which are mixed in a conventional manner. In general,the desired amount of the components used in lesser amount is dissolvedin the components making up the principal constituent, advantageously atelevated temperature. If the selected temperature is above the clearingpoint of the principal constituent, the completion of the dissolutionprocess is particularly easy to observe. However, it is also possible toprepare the liquid-crystal mixtures in other conventional ways, forexample using premixes or from a so-called “multibottle system”.

By means of suitable additives, the liquid-crystal phases according tothe invention can be modified in such a way that they can be employed inany type of LCD that has been disclosed hitherto and in particular inECB displays, VA displays, PA LCDs, ASM LCDs and IPS displays.

The examples below serve to illustrate the invention without restrictingit. In the examples, the melting point T (C,N), the transition from thesmectic (S) phase to the nematic (N) phase T(S,N) and the clearing pointT (N,I) of a liquid-crystal substance are indicated in degrees Celsius.The percentages above and below are, unless explicitly stated otherwise,percent by weight, and the physical properties are the values at 20° C.,unless explicitly stated otherwise.

All the indicated values for temperatures in this application are ° C.and all temperature differences are correspondingly differentialdegrees, unless explicitly stated otherwise.

In the present application and in the examples below, the structures ofthe liquid-crystal compounds are indicated by means of acronyms, thetransformation into chemical formulae taking place in accordance withTables A and B below. All radicals C_(n)H_(2n+1) and C_(m)H_(2m+1) arestraight-chain alkyl radicals having n and m C atoms respectively. Thecoding in Table B is self-evident. In Table A, only the acronym for theparent structure is indicated. In individual cases, the acronym for theparent structure is followed, separated by a hyphen, by a code for thesubstituents R¹, R², L¹ and L²:

Code for R¹, R², L¹, L² R¹ R² L¹ L² nm C_(n)H_(2n+1) C_(m)H_(2m+1) H HnOm C_(n)H_(2n+1) OC_(m)H_(2m+1) H H nO.m OC_(n)H_(2n+1) C_(m)H_(2m+1) HH n C_(n)H_(2n+1) CN H H nN.F C_(n)H_(2n+1) CN H F nN.F.F C_(n)H_(2n+1)CN F F nF C_(n)H_(2n+1) F H H nOF OC_(n)H_(2n+1) F H H nF.FC_(n)H_(2n+1) F H F nF.F.F C_(n)H_(2n+1) F F F nmF C_(n)H_(2n+1)C_(m)H_(2m+1) F H nCF₃ C_(n)H_(2n+1) CF₃ H H nOCF₃ C_(n)H_(2n+1) OCF₃ HH nOCF₃.F C_(n)H_(2n+1) OCF₃ H F nOCF₃.F.F C_(n)H_(2n+1) OCF₃ F FnOCF₂.F C_(n)H_(2n+1) OCHF₂ H H nOCF₂.F C_(n)H_(2n+1) OCHF₂ H FnOCF₂.F.F C_(n)H_(2n+1) OCHF₂ F F nS C_(n)H_(2n+1) NCS H H rVsNC_(r)H_(2r+1)—CH═CH—C_(s)H_(2s)— CN H H nEsNC_(r)H_(2r+1)—O—C_(s)H_(2s)— CN H H nAm C_(n)H_(2n+1) COOC_(m)H_(2m+1) HH nCl C_(n)H_(2n+1) Cl H H nCl.F C_(n)H_(2n+1) Cl H F nCl.F.FC_(n)H_(2n+1) Cl F F

TABLE A

PCH

PDX

BCH

CBC

CCH

CCP

CP

CPTP

CEPTP

D

ECCP

CECP

EPCH

HP

ME

PYP

PYRP

PTP

BECH

EBCH

CPC

EHP

BEP

ET

TABLE B

CCZU-n-X (X = F, Cl, —OCF₂H, —OCF₃)

CDU-n-X (X = F, Cl, —OCF₂H, —OCF₃)

T15

K3n

M3n

CGP-n-X (X = F, Cl, —OCF₂H, —OCH₃)

Inm

CGU-n-X (X = F, Cl, —OCF₂H, —OCF₃)

PGU-n-X (X = F, Cl, —OCF₂H, —OCF₃)

C-nm

C15

CB15

S-811

S-1011

S-2011

CBC-nmF

CCN-nm

G3n

CCEPC-nm

CCPC-nm

CH-nm

HD-nm

HH-nm

NCB-nm

OS-nm

CHE

CBC-nmF

ECBC-nm

ECCH-nm

CCH-n1EM

T-nFN

B-nO.FN

CVCC-n-m

CVCP-n-m

CP-V-N

CVCVC-n-m

CC-n-V

CCG-V-F

CCP-nV2-m

CCP-V-m

CCP-V2-m

CCP-V-m

CCP-nV-m

CCP-V2-m

CC-V-V

CC-1V-V

CC-1V-V1

CC-2V-V

CC-2V-V2

CC-2V-V1

CC-V1-V

CC-V1-1V

CC-V2-1V

PCH-n(O)mFF

CCP-n(O)mFF

CCQU-n-X (X = F, Cl, —OCF₂H, —OCH₃)

PUQU-n-X (X = F, Cl, —OCF₂H, —OCH₃)

EXAMPLES

The following examples are intended to explain the invention withoutlimiting it. Above and below, percentages are percent by weight. Alltemperatures are given in degrees Celsius. An denotes the opticalanisotropy (589 nm, 20° C.), Δ∈ the dielectric anisotropy (1 kHz, 20°C.), H.R. the voltage holding ratio (at 100° C., after 5 minutes in theoven, 1 V), and V₁₀, V₅₀ and V₉₀ the threshold voltage, mid-grey voltageand saturation voltage respectively, and the capacitive thresholdvoltage V₀ were determined at 20° C.

Substance Examples Example 1 Preparation of Chiral3,5-di-tert-butyl-3′,5′-difluoro-4′-(1-methylheptyloxy)biphenyl-4-olStep 1: Preparation of 3,5-difluoro-4-(1-methylheptyloxy)bromobenzene

12.0 g of 4-bromo-2,6-difluorophenol, 10.0 ml of (S)-(+)-2-octanol and16.5 g of triphenylphosphine were dissolved in 300 ml of tetrahydrofuranat about 20° C. with stirring under a nitrogen atmosphere. 12.5 ml ofanhydrous (max. 0.0075% of H₂O) diisopropyl azodicarboxylate weresubsequently added dropwise. The reaction proceeds exothermically. Therate of addition was selected in such a way that the temperature of themixture did not exceed 45° C. The reaction solution was subsequentlystirred for 2 h, and the solvent was then removed in a rotaryevaporator. The crude product was purified in a mixture of chlorobutaneand heptane in the ratio 1:1 over 2 l of silica gel, giving 14.5 g of3,5-difluoro-4-(1-methylheptyloxy)bromobenzene as a clear liquid.

Step 2: Preparation of 3,5-difluoro-4-(1-methylheptyloxy)phenylboronicacid

14.5 g of 1-bromo-3,5-difluoro-4-(1-methylheptyloxy)benzene from step 1were dissolved in 150 ml of diethyl ether and cooled to −70° C. At thistemperature, with cooling, firstly 31.0 ml of a 15% solution ofbutyllithium in n-hexane were slowly added dropwise, the mixture wasstirred at the same temperature for 1 h, and then 5.6 ml of trimethylborate were slowly added dropwise, and the mixture was stirred for afurther h. The temperature of the reaction solution was slowly allowedto rise to −10° C. The mixture was then hydrolysed with distilled water,and the pH was adjusted to 2 using hydrochloric acid. The organic phasewas separated off, and the aqueous phase was extracted with MTB ether.The product was subjected to conventional purification and dried overNa₂SO₄, giving 13.9 g of 3,5-difluoro-4-(1-methylheptyloxy)phenylboronicacid.

Step 3: Preparation of3,5-di-tert-butyl-3′,5′-difluoro-4′-(1-methylheptyloxy)biphenyl-4-ol

3,5-Difluoro-4-(1-methylheptyloxy)phenylboronic acid from step 2 weredissolved in 100 ml of 2-propanol with 12.0 g of2,6-di-tert-butyl-4-bromophenol, 30 mg of palladium(II) acetate and 100mg of triphenylphosphine, and 30 ml of 2 molar aqueous sodium carbonatesolution and 20 ml of distilled water were added. The mixture was thenrefluxed at 80° C. for 15 h. The reaction mixture was then cooled toabout 20° C. and diluted with water. MBT ether was added, and theorganic phase was separated off. The product was subjected toconventional purification.

8.4 g of3,5-di-tert-butyl-3′,5′-difluoro-4′-(1-methylheptyloxy)biphenyl-4-olwere obtained as a colourless oil having a glass transition temperatureof −21° C.

Examples 2 to 54

The following are prepared analogously to Example 1:

where W and Z denote H.

No. Config.^(§) R¹¹ R¹² X Y Properties 2 S C₂H₅ CH₃ H H 3 S n-C₃H₇ CH₃ HH 4 S n-C₄H₉ CH₃ H H 5 S n-C₅H₁₁ CH₃ H H 6 S n-C₆H₁₃ CH₃ H H 7 S n-C₃H₇C₂H₅ H H 8 S n-C₄H₉ C₂H₅ H H 9 S n-C₅H₁₁ C₂H₅ H H 10 S n-C₆H₁₃ C₂H₅ H H11 S C₂H₅ CH₃ F H 12 S n-C₃H₇ CH₃ F H 13 S n-C₄H₉ CH₃ F H 14 S n-C₅H₁₁CH₃ F H 15 S n-C₆H₁₃ CH₃ F H 16 S n-C₃H₇ C₂H₅ F H 17 S n-C₄H₉ C₂H₅ F H18 S n-C₅H₁₁ C₂H₅ F H 19 S n-C₆H₁₃ C₂H₅ F H 20 S C₂H₅ CH₃ F F 21 Sn-C₃H₇ CH₃ F F 22 S n-C₄H₉ CH₃ F F 23 S n-C₅H₁₁ CH₃ F F Note:^(§)Configuration of the alcohol employed.

No. Config.^(§) R¹¹ R¹² X Y 1 S n-C₆H₁₃ CH₃ F F 24 S n-C₃H₇ C₂H₅ F F 25S n-C₄H₉ C₂H₅ F F 26 S n-C₅H₁₁ C₂H₅ F F 27 S n-C₆H₁₃ C₂H₅ F F 28 R C₂H₅CH₃ H H 29 R n-C₃H₇ CH₃ H H 30 R n-C₄H₉ CH₃ H H 31 R n-C₅H₁₁ CH₃ H H 32R n-C₆H₁₃ CH₃ H H 33 R n-C₃H₇ C₂H₅ H H 34 R n-C₄H₉ C₂H₅ H H 35 R n-C₅H₁₁C₂H₅ H H 36 R n-C₆H₁₃ C₂H₅ H H 37 R C₂H₅ CH₃ F H 38 R n-C₃H₇ CH₃ F H 39R n-C₄H₉ CH₃ F H 40 R n-C₅H₁₁ CH₃ F H 41 R n-C₆H₁₃ CH₃ F H 42 R n-C₃H₇C₂H₅ F H 43 R n-C₄H₉ C₂H₅ F H 44 R n-C₅H₁₁ C₂H₅ F H 45 R n-C₆H₁₃ C₂H₅ FH 46 R C₂H₅ CH₃ F F 47 R n-C₃H₇ CH₃ F F 48 R n-C₄H₉ CH₃ F F 49 R n-C₅H₁₁CH₃ F F 50 R n-C₆H₁₃ CH₃ F F 51 R n-C₃H₇ C₂H₅ F F 52 R n-C₄H₉ C₂H₅ F F53 R n-C₅H₁₁ C₂H₅ F F 54 R n-C₆H₁₃ C₂H₅ F F Note: ^(§)Configuration ofthe alcohol employed.

Examples 55 to 72

The following are prepared analogously to Example 1:

No. Config.^(§) R¹¹ R¹² 55 S C₂H₅ CH₃ 56 S n-C₃H₇ CH₃ 57 S n-C₄H₉ CH₃ 58S n-C₅H₁₁ CH₃ 59 S n-C₆H₁₃ CH₃ 60 S n-C₃H₇ C₂H₅ 61 S n-C₄H₉ C₂H₅ 62 Sn-C₅H₁₁ C₂H₅ 63 S n-C₆H₁₃ C₂H₅ 64 R C₂H₅ CH₃ 65 R n-C₃H₇ CH₃ 66 R n-C₄H₉CH₃ 67 R n-C₅H₁₁ CH₃ 68 R n-C₆H₁₃ CH₃ 69 R n-C₃H₇ C₂H₅ 70 R n-C₄H₉ C₂H₅71 R n-C₅H₁₁ C₂H₅ 72 R n-C₆H₁₃ C₂H₅ Note: ^(§)Configuration of thealcohol employed.

Examples 73 to 126

The following are prepared analogously to Example 1:

where W and Z denote H.

No. Config.^(§) R¹¹ R¹² X Y 73 S C₂H₅ CH₃ H H 74 S n-C₃H₇ CH₃ H H 75 Sn-C₄H₉ CH₃ H H 76 S n-C₅H₁₁ CH₃ H H 77 S n-C₆H₁₃ CH₃ H H 78 S n-C₃H₇C₂H₅ H H 79 S n-C₄H₉ C₂H₅ H H 80 S n-C₅H₁₁ C₂H₅ H H 81 S n-C₆H₁₃ C₂H₅ HH 82 S C₂H₅ CH₃ F H 83 S n-C₃H₇ CH₃ F H 84 S n-C₄H₉ CH₃ F H 85 S n-C₅H₁₁CH₃ F H 86 S n-C₆H₁₃ CH₃ F H 87 S n-C₃H₇ C₂H₅ F H 88 S n-C₄H₉ C₂H₅ F H89 S n-C₅H₁₁ C₂H₅ F H 90 S n-C₆H₁₃ C₂H₅ F H 91 S C₂H₅ CH₃ F F 92 Sn-C₃H₇ CH₃ F F 92 S n-C₄H₉ CH₃ F F 94 S n-C₅H₁₁ CH₃ F F 95 S n-C₆H₁₃ CH₃F F 96 S n-C₃H₇ C₂H₅ F F 97 S n-C₄H₉ C₂H₅ F F 98 S n-C₅H₁₁ C₂H₅ F F 99 Sn-C₆H₁₃ C₂H₅ F F 100 R C₂H₅ CH₃ H H 101 R n-C₃H₇ CH₃ H H 102 R n-C₄H₉CH₃ H H 103 R n-C₅H₁₁ CH₃ H H 104 R n-C₆H₁₃ CH₃ H H 105 R n-C₃H₇ C₂H₅ HH 106 R n-C₄H₉ C₂H₅ H H 107 R n-C₅H₁₁ C₂H₅ H H 108 R n-C₆H₁₃ C₂H₅ H H109 R C₂H₅ CH₃ F H 110 R n-C₃H₇ CH₃ F H 111 R n-C₄H₉ CH₃ F H 112 Rn-C₅H₁₁ CH₃ F H 113 R n-C₆H₁₃ CH₃ F H 114 R n-C₃H₇ C₂H₅ F H 115 R n-C₄H₉C₂H₅ F H 116 R n-C₅H₁₁ C₂H₅ F H 117 R n-C₆H₁₃ C₂H₅ F H 118 R C₂H₅ CH₃ FF 119 R n-C₃H₇ CH₃ F F 129 R n-C₄H₉ CH₃ F F 121 R n-C₅H₁₁ CH₃ F F 122 Rn-C₆H₁₃ CH₃ F F 123 R n-C₃H₇ C₂H₅ F F 124 R n-C₄H₉ C₂H₅ F F 125 Rn-C₅H₁₁ C₂H₅ F F 126 R n-C₆H₁₃ C₂H₅ F F Note: ^(§)Configuration of thealcohol employed.

Examples 127 to 180

The following are prepared analogously to Example 1:

where W and Z denote H.

No. R¹¹ R¹² X Y Config.^(§) 127 S C₂H₅ CH₃ H H 128 S n-C₃H₇ CH₃ H H 129S n-C₄H₉ CH₃ H H 130 S n-C₅H₁₁ CH₃ H H 131 S n-C₆H₁₃ CH₃ H H 132 Sn-C₃H₇ C₂H₅ H H 133 S n-C₄H₉ C₂H₅ H H 134 S n-C₅H₁₁ C₂H₅ H H 135 Sn-C₆H₁₃ C₂H₅ H H 136 S C₂H₅ CH₃ F H 137 S n-C₃H₇ CH₃ F H 138 S n-C₄H₉CH₃ F H 139 S n-C₅H₁₁ CH₃ F H 140 S n-C₆H₁₃ CH₃ F H 141 S n-C₃H₇ C₂H₅ FH 142 S n-C₄H₉ C₂H₅ F H 143 S n-C₅H₁₁ C₂H₅ F H 144 S n-C₆H₁₃ C₂H₅ F H145 S C₂H₅ CH₃ F F 146 S n-C₃H₇ CH₃ F F 147 S n-C₄H₉ CH₃ F F X 148 Sn-C₅H₁₁ CH₃ F F 149 S n-C₆H₁₃ CH₃ F F 150 S n-C₃H₇ C₂H₅ F F 151 S n-C₄H₉C₂H₅ F F 152 S n-C₅H₁₁ C₂H₅ F F 153 S n-C₆H₁₃ C₂H₅ F F 154 R C₂H₅ CH₃ HH 155 R n-C₃H₇ CH₃ H H 156 R n-C₄H₉ CH₃ H H 157 R n-C₅H₁₁ CH₃ H H 158 Rn-C₆H₁₃ CH₃ H H 159 R n-C₃H₇ C₂H₅ H H 160 R n-C₄H₉ C₂H₅ H H 161 Rn-C₅H₁₁ C₂H₅ H H 162 R n-C₆H₁₃ C₂H₅ H H 163 R C₂H₅ CH₃ F H 164 R n-C₃H₇CH₃ F H 165 R n-C₄H₉ CH₃ F H 166 R n-C₅H₁₁ CH₃ F H 167 R n-C₆H₁₃ CH₃ F H168 R n-C₃H₇ C₂H₅ F H 169 R n-C₄H₉ C₂H₅ F H 170 R n-C₅H₁₁ C₂H₅ F H 171 Rn-C₆H₁₃ C₂H₅ F H 172 R C₂H₅ CH₃ F F 173 R n-C₃H₇ CH₃ F F 174 R n-C₄H₉CH₃ F F 175 R n-C₅H₁₁ CH₃ F F 176 R n-C₆H₁₃ CH₃ F F 177 R n-C₃H₇ C₂H₅ FF 178 R n-C₄H₉ C₂H₅ F F 179 R n-C₅H₁₁ C₂H₅ F F 180 R n-C₆H₁₃ C₂H₅ F FNote: ^(§)Configuration of the alcohol employed.

Use Examples

The properties of the compounds according to the invention areinvestigated. To this end, liquid-crystal mixtures are prepared, and thecorresponding compounds are added.

Use Example 1

A nematic liquid-crystal mixture (M0) having the following compositionand physical properties is prepared.

Compound/ Concentration/ abbreviation % by weight Physical propertiesPCH-5F 8.0 Clearing point (N, I) = 80.5° C. PCH-6F 6.4 PCH-7F 4.8CCP-2OCF₃ 6.4 CCP-3OCF₃ 9.6 CCP-4OCF₃ 5.6 CCP-5OCF₃ 8.8 BCH-3F.F 9.6BCH-5F.F 8.0 ECCP-3OCF₃ 4.0 ECCP-3OCF₃ 4.0 CC-4-V 20.0 CBC-33F 1.6CBC-53F 1.6 CBC-55F 1.6 Σ 100.0

0.5% of the compound of Example 1 are added to this liquid-crystalmixture (M0). The clearing point of the mixture (M1) drops to 78.6° C.This doped mixture, M1, is heated in an open capillary tube (MettlerME-18 552) at a fill level of 1 cm, at 150° C. in the presence ofatmospheric oxygen. After the pre-specified times, the clearing point ofthe sample is determined in the capillary tube. The capillary tube isthen re-heated to 150° C. For comparison, the same investigation iscarried out on the undoped mixture, M0. The results of thisinvestigation are shown in the following table.

Mixture M0 M1 c(B1)/% 0 0.5 |P|/μm ∞* 74 HTP/μm⁻¹ n.a. 2.7 t/h T(N, I)/°C.  0 80.5 78.6  1 79.4 78.9  2 79.5 78.8  5 76.8 78.8 10 74.0 78.9 3063.7 78.7 50 59.9 78.4 Notes: *cannot be determined n.a. not applicable.

The measurement accuracy in the determination of the clearing point was+/−0.3 degree.

Mixture M1 has excellent technical properties and is distinguished, inparticular, by very good thermal stability, in particular in thepresence of atmospheric oxygen.

In the case of the undoped mixture (M0), the clearing point drops bymore than twenty differential degrees over the course of somewhat morethan four days in the stability test described above. By contrast, theclearing point of the mixture according to the invention drops onlyinsignificantly, by 0.2 differential degree.

Comparative Example C1

0.5% of the chiral dopant S-811 from Merck KGaA are added to themixture, M0, described under Use Example 1. The resultant mixture, C1,has a clearing point of 79.0° C. and a cholesteric pitch of 17 μm. Underthe thermal load described under Use Example 1, the clearing point ofthe mixture C1 drops significantly to 60.0° C. within 50 h.

Comparative Example C2

0.5% of the Achiral Phenol AP

from DE 195 391 41 having a melting point of 91° C. are added to themixture, M0, described under Use Example 1. The resultant mixture, C2,has a clearing point of 78.2° C. Under the thermal load described underUse Example 1, the clearing point of mixture C2 drops onlyinsignificantly, to 78.0° C. Since the added compound is achiral,mixture C2 is likewise not chiral and thus has no cholesteric pitch.

These results are shown in the following table.

Comparative Examples Example —/— 1 and 2 Use Example 1 Mixture M0 C1 C2M1 Dopant —/— S-811 AP B1 |P|/μm ∞* 17 ∞* 74 ΔT^(§)/° 20.6 19.0 0.2 0.2Notes: *cannot be determined, ^(§)ΔT ≡ T(N, I), (50 h) − T(N, I), (0 h)

1. A compound of formula I

in which R*¹ is a chiral radical, Z¹ is, if present more than once, ineach case, independently of one another, —CH₂—CH₂—, —CH═CH—, —C≡C—,—COO—, —OCO—, —CH₂O—, —OCH₂—, —CF₂O—, —OCF₂—, —(CH₂)₄—, —CF═CF—,—CH═CF—, —CF═CH—, —CH₂—, —CF₂—, —CHF—, —O—, —S— or a single bond,

is, if present more than once, in each case, independently of oneanother, (a) a trans-1,4-cyclohexylene radical, in which one or morenon-adjacent CH₂ groups are optionally replaced by —O— and/or —S—, (b) a1,4-cyclohexenylene radical, (c) a 1,4-phenylene radical, in which oneor two CH groups are optionally replaced by N, or (d)1,4-bicyclo[2.2.2]octylene, piperidine-1,4-diyl, naphthalene-2,6-diyl,decahydronaphthalene-2,6-diyl, or1,2,3,4-tetrahydronaphthalene-2,6-diyl, where these radicals (a) to (d)and the phenolic benzene ring is optionally mono- or polysubstituted byF atoms, and n¹ is 1, 2 or 3, wherein A) R*¹ is a chiral radical of thefollowing formula

in which K is a single bond, alkylene having 1 to 9 C atoms, alkenyleneor alkynylene having 2 to 9 C atoms, wherein one, two or more of the—CH₂— groups present in the alkylene, alkenylene or alkynylene areoptionally replaced by —O—, —C═O— or —S—, but where no two O atoms arebonded directly to one another, and the alkylene, alkenylene oralkynylene are optionally substituted by halogen, or R*¹ is

Q is H or halogen, n and m are different from one another and,independently of one another, are 1 to 11, p is 0 or 1, and L, M and N,each, independently of one another, but differently from one another andfrom

are hydrogen, halogen, aryl or cycloalkyl, alkyl or alkoxy having 1 to11 C atoms, alkenyl, alkenyloxy, alkynyl or alkynyloxy having 2 to 11 Catoms, where one, two or more of the —CH₂— groups present in the alkyl,alkoxy, alkenyl, alkenyloxy, alkynyl or alkynyloxy are optionallyreplaced by —O—, —C═O— or —S—, but where no two O atoms are bondeddirectly to one another and the alkyl, alkoxy, alkenyl, alkenyloxy,alkynyl or alkynyloxy are optionally substituted by halogen; or B) R*¹is a chiral radical of one of the following formulae

in which Q is H or halogen, n and m are different from one another and,independently of one another, are 1 to 11, p is 0 or 1, and r is 0 to 4.2. A compound according to claim 1, which is capable of inducing acholesteric phase in a nematic liquid crystal and simultaneously actingas a stabiliser.
 3. A compound according to claim 1, which is capable ofacting as a free-radical scavenger.
 4. A compound of formula Ia

in which

is, if present more than once, in each case, independently of oneanother, (a) a trans-1,4-cyclohexylene radical, in which one or morenon-adjacent CH₂ groups are optionally replaced by —O— and/or —S—, (b) a1,4-cyclohexenylene radical, (c) a 1,4-phenylene radical, in which oneor two CH groups are optionally replaced by N, or (d)1,4-bicyclo[2.2.2]octylene, piperidine-1,4-diyl, naphthalene-2,6-diyl,decahydronaphthalene-2,6-diyl, or1,2,3,4-tetrahydronaphthalene-2,6-diyl, where these radicals (a) to (d)and the phenolic benzene ring is optionally mono- or polysubstituted byF atoms, R*¹ is a chiral radical, Z¹¹ and Z¹² are, each independently,and in case if Z¹¹ present more than once, in each case, independentlyof one another, —CH₂—CH₂—, —CH═CH—, —C≡C—, —COO—, —OCO—, —CH₂O—, —OCH₂—,—CF₂O—, —OCF₂—, —(CH₂)₄—, —CF═CF—, —CH═CF—, —CF═CH—, —CH₂—, —CF₂—,—CHF—, —O—, —S— or a single bond, n¹¹ is 0, 1 or 2, W and Z are each,independently of one another, H, F, Cl, or alkoxy, and X and Y are each,independently of one another, H, F, Cl, alkyl or alkoxy, wherein A) thecompound of formula Ia is

or B) R*¹ is a chiral radical of the following formula

in which K is a single bond, alkylene having 1 to 9 C atoms, alkenyleneor alkynylene having 2 to 9 C atoms, wherein one, two or more of the—CH₂— groups present in the alkylene, alkenylene or alkynylene areoptionally replaced by —O—, —C═O— or —S—, but where no two O atoms arebonded directly to one another, and the alkylene, alkenylene oralkynylene are optionally substituted by halogen, or R*¹ is

Q is H or halogen, n and m are different from one another and,independently of one another, are 1 to 11, p is 0 or 1, and L, M and N,each, independently of one another, but differently from one another andfrom

are hydrogen, halogen, aryl or cycloalkyl, alkyl or alkoxy having 1 to11 C atoms, alkenyl, alkenyloxy, alkynyl or alkynyloxy having 2 to 11 Catoms, where one, two or more of the —CH₂— groups present in the alkyl,alkoxy, alkenyl, alkenyloxy, alkynyl or alkynyloxy are optionallyreplaced by —O—, —C═O— or —S—, but where no two O atoms are bondeddirectly to one another and the alkyl, alkoxy, alkenyl, alkenyloxy,alkynyl or alkynyloxy are optionally substituted by halogen; Or C) R*¹is a chiral radical of one of the following formulae

in which Q is H or halogen, n and m are different from one another and,independently of one another, are 1 to 11, p is 0 or 1, and r is 0 to 4,and wherein one of the following conditions I, II, III, IV or V must besatisfied I) wherein the compound is

or II) wherein R*¹ is a chiral radical of the following formula

in which K is a single bond, alkylene having 1 to 9 C atoms, alkenyleneor alkynylene having 2 to 9 C atoms, wherein one, two or more of the—CH₂— groups present in the alkylene, alkenylene or alkynylene areoptionally replaced by —O—, —C═O— or —S—, but where no two O atoms arebonded directly to one another, and the alkylene, alkenylene oralkynylene are optionally substituted by halogen, or R*¹ is

Q is H or halogen, n and m are different from one another and,independently of one another, are 1 to 11, p is 0 or 1, and L, M and N,each, independently of one another, but differently from one another andfrom

are hydrogen, halogen, aryl or cycloalkyl, alkyl or alkoxy having 1 to11 C atoms, alkenyl, alkenyloxy, alkynyl or alkynyloxy having 2 to 11 Catoms, where one, two or more of the —CH₂— groups present in the alkyl,alkoxy, alkenyl, alkenyloxy, alkynyl or alkynyloxy are optionallyreplaced by —O—, —CO— or —S—, but where no two O atoms are bondeddirectly to one another and the alkyl, alkoxy, alkenyl, alkenyloxy,alkynyl or alkynyloxy are optionally substituted by halogen; or III)wherein R*¹ is a chiral radical of one of the following formulae

in which Q is H or halogen, n and m are different from one another and,independently of one another, are 1 to 11, p is 0 or 1, and r is 0 to 4;or IV) wherein W and Z are each, independently of one another, H, F orCl; or V) wherein W and Z are both H.
 5. A compound according to claim1, wherein R*¹ is a chiral radical of the following formula

in which K is a single bond, alkylene having 1 to 9 C atoms, alkenyleneor alkynylene having 2 to 9 C atoms, wherein one, two or more of the—CH₂— groups present in the alkylene, alkenylene or alkynylene areoptionally replaced by —O—, —C═O— or —S—, but where no two O atoms arebonded directly to one another, and the alkylene, alkenylene oralkynylene are optionally substituted by halogen, or R*¹ is

Q is H or halogen, n and m are different from one another and,independently of one another, are 1 to 11, p is 0 or 1, and L, M and N,each, independently of one another, but differently from one another andfrom

are hydrogen, halogen, aryl or cycloalkyl, alkyl or alkoxy having 1 to11 C atoms, alkenyl, alkenyloxy, alkynyl or alkynyloxy having 2 to 11 Catoms, where one, two or more of the —CH₂— groups present in the alkyl,alkoxy, alkenyl, alkenyloxy, alkynyl or alkynyloxy are optionallyreplaced by —O—, —C═O— or —S—, but where no two O atoms are bondeddirectly to one another and the alkyl, alkoxy, alkenyl, alkenyloxy,alkynyl or alkynyloxy are optionally substituted by halogen.
 6. Acompound according to claim 1, wherein R*¹ is a chiral radical of one ofthe following formulae

in which Q is H or halogen, n and m are different from one another and,independently of one another, are 1 to 11, p is 0 or 1, and r is 0 to 4.7. A compound of formula Ia-2, Ia-3, Ia-4, Ia-5, Ia-6, Ia-7, Ia-8, orIa-9

wherein W, X, Y and Z are each, independently of one another, H, F, Cl,alkyl or alkoxy, R*¹ is a chiral radical; wherein A) R*¹ is a chiralradical of the following formula

in which K is a single bond, alkylene having 1 to 9 C atoms, alkenyleneor alkynylene having 2 to 9 C atoms, wherein one, two or more of the—CH₂— groups present in the alkylene, alkenylene or alkynylene areoptionally replaced by —O—, —C═O— or —S—, but where no two O atoms arebonded directly to one another, and the alkylene, alkenylene oralkynylene are optionally substituted by halogen, or R*¹ is

Q is H or halogen, n and m are different from one another and,independently of one another, are 1 to 11, p is 0 or 1, and L, M and N,each, independently of one another, but differently from one another andfrom

are hydrogen, halogen, aryl or cycloalkyl, alkyl or alkoxy having 1 to11 C atoms, alkenyl, alkenyloxy, alkynyl or alkynyloxy having 2 to 11 Catoms, where one, two or more of the —CH₂— groups present in the alkyl,alkoxy, alkenyl, alkenyloxy, alkynyl or alkynyloxy are optionallyreplaced by —O—, —C═O— or —S—, but where no two O atoms are bondeddirectly to one another and the alkyl, alkoxy, alkenyl, alkenyloxy,alkynyl or alkynyloxy are optionally substituted by halogen; or B) R*¹is a chiral radical of one of the following formulae

in which Q is H or halogen, n and m are different from one another and,independently of one another, are 1 to 11, p is 0 or 1, and r is 0 to 4.8. A method of providing a chiral dopant, or a stabiliser, or a chiraldopant and simultaneously a stabiliser to a liquid crystal mixture,comprising adding a compounds according to claim 1 to said liquidcrystal mixture.
 9. A liquid-crystal medium comprising a compoundaccording to claim
 1. 10. An electro-optical display comprising aliquid-crystal medium which comprises a compound according to claim 1.11. A process for preparing a liquid-crystal mixture, comprising mixingtogether a compound of formula I according to claim 1 with one or moreliquid-crystal compounds other than a compound of formula I to form aliquid-crystal mixture.
 12. A compound according to claim 4, which is


13. A compound according to claim 4, wherein R*¹ is a chiral radical ofthe following formula

in which K is a single bond, alkylene having 1 to 9 C atoms, alkenyleneor alkynylene having 2 to 9 C atoms, wherein one, two or more of the—CH₂— groups present in the alkylene, alkenylene or alkynylene areoptionally replaced by —O—, —C═O— or —S—, but where no two O atoms arebonded directly to one another, and the alkylene, alkenylene oralkynylene are optionally substituted by halogen, or R*¹ is

Q is H or halogen, n and m are different from one another and,independently of one another, are 1 to 11, p is 0 or 1, and L, M and N,each, independently of one another, but differently from one another andfrom

are hydrogen, halogen, aryl or cycloalkyl, alkyl or alkoxy having 1 to11 C atoms, alkenyl, alkenyloxy, alkynyl or alkynyloxy having 2 to 11 Catoms, where one, two or more of the —CH₂— groups present in the alkyl,alkoxy, alkenyl, alkenyloxy, alkynyl or alkynyloxy are optionallyreplaced by —O—, —C═O— or —S—, but where no two O atoms are bondeddirectly to one another and the alkyl, alkoxy, alkenyl, alkenyloxy,alkynyl or alkynyloxy are optionally substituted by halogen.
 14. Acompound according to claim 4, wherein R*¹ is a chiral radical of one ofthe following formulae

in which Q is H or halogen, n and m are different from one another and,independently of one another, are 1 to 11, p is 0 or 1, and r is 0 to 4.15. A compound according to claim 4, wherein W and Z are each,independently of one another, H, F or Cl.
 16. A compound according toclaim 4, wherein W and Z are both H.
 17. A compound of formula I

in which R*¹ is a chiral radical of the following formula

in which K is a single bond, alkylene having 1 to 9 C atoms, alkenyleneor alkynylene having 2 to 9 C atoms, wherein one, two or more of the—CH₂— groups present in the alkylene, alkenylene or alkynylene areoptionally replaced by —O—, —C═O— or —S—, but where no two O atoms arebonded directly to one another, and the alkylene, alkenylene oralkynylene are optionally substituted by halogen, or R*¹ is a group

Q is H or halogen, n and m are different from one another and,independently of one another, are 1 to 11, p is 0 or 1, L, M and N,each, independently of one another, but differently from one another andfrom

are hydrogen, halogen, aryl or cycloalkyl, alkyl or alkoxy having 1 to11 C atoms, alkenyl, alkenyloxy, alkynyl or alkynyloxy having 2 to 11 Catoms, where one, two or more of the —CH₂— groups present in the alkyl,alkoxy, alkenyl, alkenyloxy, alkynyl or alkynyloxy are optionallyreplaced by —O—, —C═O— or —S—, but where no two O atoms are bondeddirectly to one another and the alkyl, alkoxy, alkenyl, alkenyloxy,alkynyl or alkynyloxy are optionally substituted by halogen, Z¹ is, ifpresent more than once, in each case, independently of one another,—CH₂—CH₂—, —CH═CH—, —C≡C—, —COO—, —OCO—, —CH₂O—, —OCH₂—, —CF₂O—, —OCF₂—,—(CH₂)₄—, —CF═CF—, —CH═CF—, —CF═CH—, —CH₂—, —CF₂—, —CHF—, —O—, —S— or asingle bond,

is, if present more than once, in each case, independently of oneanother, (a) a trans-1,4-cyclohexylene radical, in which one or morenon-adjacent CH₂ groups are optionally replaced by —O— and/or —S—, (b) a1,4-cyclohexenylene radical, (c) a 1,4-phenylene radical, in which oneor two CH groups are optionally replaced by N, or (d)1,4-bicyclo[2.2.2]octylene, piperidine-1,4-diyl, naphthalene-2,6-diyl,decahydronaphthalene-2,6-diyl, or1,2,3,4-tetrahydronaphthalene-2,6-diyl, where these radicals (a) to (d)and the phenolic benzene ring is optionally mono- or polysubstituted byF atoms, and n¹ is 1, 2 or
 3. 18. A compound according to claim 17,wherein R*¹ is a chiral radical of one of the following formulae

in which Q is H or halogen, n and m are different from one another and,independently of one another, are 1 to 11, p is 0 or 1, and r is 0 to 4.19. A compound according to claim 7, wherein R*¹ is a chiral radical ofthe following formula

in which K is a single bond, alkylene having 1 to 9 C atoms, alkenyleneor alkynylene having 2 to 9 C atoms, wherein one, two or more of the—CH₂— groups present in the alkylene, alkenylene or alkynylene areoptionally replaced by —O—, —C═O— or —S—, but where no two O atoms arebonded directly to one another, and the alkylene, alkenylene oralkynylene are optionally substituted by halogen, or R*¹ is

Q is H or halogen, n and m are different from one another and,independently of one another, are 1 to 11, p is 0 or 1, and L, M and N,each, independently of one another, but differently from one another andfrom

are hydrogen, halogen, aryl or cycloalkyl, alkyl or alkoxy having 1 to11 C atoms, alkenyl, alkenyloxy, alkynyl or alkynyloxy having 2 to 11 Catoms, where one, two or more of the —CH₂— groups present in the alkyl,alkoxy, alkenyl, alkenyloxy, alkynyl or alkynyloxy are optionallyreplaced by —O—, —C═O— or —S—, but where no two O atoms are bondeddirectly to one another and the alkyl, alkoxy, alkenyl, alkenyloxy,alkynyl or alkynyloxy are optionally substituted by halogen.
 20. Acompound according to claim 7, wherein R*¹ is a chiral radical of one ofthe following formulae

in which Q is H or halogen, n and m are different from one another and,independently of one another, are 1 to 11, p is 0 or 1, and r is 0 to 4.21. A compound according to claim 5, wherein K is a single bond, —CH₂—,—O—, —CO—O—, —CO—O—CH₂—, —O—CO—, —CH₂—CH₂—, —CH═CH— or —C≡C—.
 22. Acompound according to claim 13, wherein K is a single bond, —CH₂—, —O—,—CO—O—, —CO—O—CH₂—, —O—CO—, —CH₂—CH₂—, —CH═CH— or —C≡C—.
 23. A compoundaccording to claim 5, wherein L, M and N are each, independently of oneanother, hydrogen, halogen, alkyl or alkoxy having 1 to 11 C atoms,alkenyl, alkenyloxy, alkynyl or alkynyloxy having 2 to 11 C atoms, whereone, two or more of the —CH₂— groups present are optionally replaced by—O—, —C═O— or —S—, but where no two O atoms are bonded directly to oneanother, and are optionally substituted by halogen.
 24. A compoundaccording to claim 13, wherein L, M and N are each, independently of oneanother, hydrogen, halogen, alkyl or alkoxy having 1 to 11 C atoms,alkenyl, alkenyloxy, alkynyl or alkynyloxy having 2 to 11 C atoms, whereone, two or more of the —CH₂— groups present are optionally replaced by—O—, —C═O— or —S—, but where no two O atoms are bonded directly to oneanother, and are optionally substituted by halogen.
 25. A compoundaccording to claim 23, wherein L, M and N are each, independently of oneanother, hydrogen, halogen, alkyl or alkoxy having 1 to 11 C atoms,alkenyl, alkenyloxy, alkynyl or alkynyloxy having 2 to 11 C atoms.
 26. Acompound according to claim 24, wherein L, M and N are each,independently of one another, hydrogen, halogen, alkyl or alkoxy having1 to 11 C atoms, alkenyl, alkenyloxy, alkynyl or alkynyloxy having 2 to11 C atoms.
 27. A method of providing a chiral dopant, or a stabiliser,or a chiral dopant and simultaneously a stabiliser to a liquid crystalmixture, comprising adding to said liquid crystal mixture a compoundaccording to claim
 4. 28. An electro-optical display comprising aliquid-crystal medium comprising a compound according to claim
 4. 29. Anelectro-optical display comprising a liquid-crystal medium whichcomprises a compound according to claim
 7. 30. A liquid crystal mixturecontaining at least two liquid crystalline compounds one of which is acompound of formula Ia

in which

is, if present more than once, in each case, independently of oneanother, (a) a trans-1,4-cyclohexylene radical, in which one or morenon-adjacent CH₂ groups are optionally replaced by —O— and/or —S—, (b) a1,4-cyclohexenylene radical, (c) a 1,4-phenylene radical, in which oneor two CH groups are optionally replaced by N, or (d)1,4-bicyclo[2.2.2]octylene, piperidine-1,4-diyl, naphthalene-2,6-diyl,decahydronaphthalene-2,6-diyl, or1,2,3,4-tetrahydronaphthalene-2,6-diyl, where these radicals (a) to (d)and the phenolic benzene ring is optionally mono- or polysubstituted byF atoms, R*¹ is a chiral radical, Z¹¹ and Z¹² are, each independently,and in case if Z¹¹ present more than once, in each case, independentlyof one another, —CH₂—CH₂—, —CH═CH—, —C≡C—, —COO—, —OCO—, —CH₂O—, —OCH₂—,—CF₂O—, —OCF₂—, —(CH₂)₄—, —CF═CF—, —CH═CF—, —CF═CH—, —CH₂—, —CF₂—,—CHF—, —O—, —S— or a single bond, n¹¹ is 0, 1 or 2, W and Z are each,independently of one another, H, F, Cl, or alkoxy, and X and Y are each,independently of one another, H, F, Cl, alkyl or alkoxy, wherein A) thecompound of formula Ia is

or B) R*¹ is a chiral radical of the following formula

in which K is a single bond, alkylene having 1 to 9 C atoms, alkenyleneor alkynylene having 2 to 9 C atoms, wherein one, two or more of the—CH₂— groups present in the alkylene, alkenylene or alkynylene areoptionally replaced by —O—, —C═O— or —S—, but where no two O atoms arebonded directly to one another, and the alkylene, alkenylene oralkynylene are optionally substituted by halogen, or R*¹ is

Q is H or halogen, n and m are different from one another and,independently of one another, are 1 to 11, p is 0 or 1, and L, M and N,each, independently of one another, but differently from one another andfrom

are hydrogen, halogen, aryl or cycloalkyl, alkyl or alkoxy having 1 to11 C atoms, alkenyl, alkenyloxy, alkynyl or alkynyloxy having 2 to 11 Catoms, where one, two or more of the —CH₂— groups present in the alkyl,alkoxy, alkenyl, alkenyloxy, alkynyl or alkynyloxy are optionallyreplaced by —O—, —C═O— or —S—, but where no two O atoms are bondeddirectly to one another and the alkyl, alkoxy, alkenyl, alkenyloxy,alkynyl or alkynyloxy are optionally substituted by halogen; or C) R*¹is a chiral radical of one of the following formulae

in which Q is H or halogen, n and m are different from one another and,independently of one another, are 1 to 11, p is 0 or 1, and r is 0 to 4.31. A liquid crystal mixture according to claim 30, which comprises oneor more compounds of formula Ia having an absolute value for the HTP of2.7 μm⁻¹ or more.